Head directly south of Walden Pond and you should see a small area with cars stacked on top of each other in sort of like a circle the Behemoth should be walking around in this area.

Swan's Pond

This Behemoth is located at Swan's Pond just south-west of GoodNeighbour. He is a Passive/Aggressive Behemoth so he will only attack you if you Agro him.

Fort Strong

*WARNING CONTAINS SPOILER*

This is a small Spoiler but pertains to the story. if you do not want to know.

This is a scripted Behemoth kill, After joining the Brotherhood Of Steel (You must complet Reunions quest for the Prydwen to apper) The Prydwen is where you get the quest "Shadow of Steel" (Upon leaving Fort Hagen during the Reunions quest the The Prydwen will appear above and signal the start of this quest). you will get the quest from Elder Maxson, He will ask you to go to Fort Strong and clear it out. Here you will fly a vertibird to Fort Strong and you will see the Behemoth on the ground (Only appers when doing this quest).

*Video coming soon*

Med-Tek Research

This location of the Behemoth is located North-East of the Med-Tek Research building under the odd shaped tower. After reaching the back end of the building stand under the tower and head NE, head that direction till you see a car with a stuffed monkey in the car, Take this monkey wait a few seconds and the Behemoth will apper.

Note: This guide is a work-in-progress. More Super Mutant Behemoth locations will be added in this page as soon as they are discovered.